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Mo5N6 nanosheets were synthesized by a nickel-induced growth method and were found to possess peroxidase-like activity in acidic condition and catalase-like activity in weak basic condition. In acidic condition, Mo5N6 nanosheets can catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) by H2O2 to form a blue color product (TMBOX). At the co-existence of 4-aminophenol (4-AP), 4-AP can react with H2O2 and TMBOX, resulting in the decrease of TMBOX and the fading of blue color. Therefore, a facile, sensitive colorimetric method for the quantitative detection of 4-AP was developed. The linear range for 4-AP was 1.0 to 80.0 μmol⋅L‒1 (R2 = 0.999), and the detection limit was 0.56 μmol⋅L‒1 based on 3σ/k. Resorcinol, aniline, humic acid, and common ions and anions in surface water did not interfere the determination of 4-AP. This colorimetric method was applied to measure the 4-AP in real water sample from Wulong River in Fujian Province of China. The relative standard deviation for the determination of 4-AP was ranged from 0.03 to 1.88%, and the recoveries from spiked samples were ranged between 99.2 and 107.6%. The determination results were consistent with those obtained by HPLC. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cu-g-C 3 N 5 nanozyme with efficient laccase-like activity was proposed. • Triazole groups improve the stability of Cu NPs and facilitate the activation of O 2. • Cu-g-C 3 N 5 nanozyme displays robust catalytic activity. • Cu-g-C 3 N 5 nanozyme was applied for colorimetric detection of BPA. Herein, a new strategy for laccase-like nanozyme is proposed by utilizing copper nanoparticles (Cu NPs) as the active center, carbon nitride as the skeleton and triazole groups as the cofactor. Cu NPs incorporated nitrogen-rich carbon nitride (Cu-g-C 3 N 5) nanocomposites are found to possess excellent laccase-like activity, which can catalyze the oxidation of bisphenol A (BPA) to produce a color change in the presence of 4-aminoantipyrine. The catalytic efficiency of Cu-g-C 3 N 5 nanocomposites is 4-fold higher than their analogue (Cu-g-C 3 N 4 nanocomposites) without triazole groups. Cu-g-C 3 N 5 nanocomposites also display robust catalytic activity with high temperature stability, resistance to acid and alkalinity, and long term stability. Density functional theory calculations indicate that triazole groups are beneficial to improve the stability of Cu NPs via additional Cu-N bonds and facilitate the activation of the adsorbed O 2 molecules. There is a linear relationship between the absorbance and BPA concentration over the range of 0.25–25 mg L−1 with the limit of detection of 0.09 mg L−1. Finally, Cu-g-C 3 N 5 nanocomposites are successfully applied for colorimetric detection of BPA released from polycarbonate microplastics. To the best of our knowledge, this is the first example to utilize laccase-like nanozyme for colorimetric detection of BPA. [ABSTRACT FROM AUTHOR]